This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-202185 filed on Jul. 4, 2000, Japanese Patent Application No. 2000-202186 filed on Jul. 4, 2000, Japanese Patent Application No. 2001-71925 filed on Mar. 14,2001 and Japanese Patent Application No. 2001-135715 filed on May 7, 2001.
1. Field of the Invention
The present invention relates to a rotational-position sensing device and a windshield wiper system.
2. Description of Related Art
FIG. 26 shows a rotational-position sensing device for a windshield wiper system disclosed in Japanese Unexamined Utility Model Publication No. 61-35068. A worm 1 and a wheel (acting as a rotator) 2 meshed with the worm 1 constitute a speed reducing gear mechanism. Rotation of an output shaft 3 secured to the wheel 2 is transmitted to a crank mechanism (not shown) acting as a reciprocating swing mechanism. The crank mechanism reciprocally swings wiper blades (not shown) along a windshield.
A cover 4 that covers a gear case opposes the wheel 2. A follower 5 is rotatably supported by a spindle 4a that protrudes from the cover 4. A switching pattern 6 is arranged in an opposing surface of the follower 5 that opposes the cover 4. A plurality of contact terminals 7 are arranged in an opposing surface of the cover 4 that opposes the follower 5. The rotation of the wheel 2, which generates the swing motion of the wiper blades, is transmitted to the follower 5 through engagement between a protrusion 8 of the wheel 2 and a protrusion 9 of the follower 5, so that the follower 5 is integrally rotated with the wheel 2. As the follower 5 rotates, the contact terminals 7 engage and disengage with the switching pattern 6, so that a rotational position of the wheel 2 or a rotational position of the output shaft 3 is sensed or detected.
The contact terminals 7 are urged against the switching pattern 6 because of their own resilient forces. When the resilient forces of the contact terminals 7 are summed and are applied to the follower 5 to lever the follower 5 about the spindle 4a, the follower 5 tilts with respect to the spindle 4a. When the follower 5 tilts, the follower 5 cannot rotate freely, causing an increased rotational resistance of the follower 5. The increase in the rotational resistance of the follower 5 normally results in a decrease in a transmission efficiency of the power transmission system between a wiper drive motor and the follower 5. Furthermore, the tilt of the follower 5 may cause a contact failure between the contact terminals 7 and the switching pattern 6. Such a contact failure causes a reduction in a sensing accuracy of the rotational-position sensing device.
To restrain the tilt of the follower 5, a wave washer 61 is inserted around the spindle 4a to urge the follower 5 in an axial direction away from it, and a stationary engaging member 62, such as a C-ring, is fitted around the spindle 4a to hold the follower 5 in place around the spindle 4a. 
However, when an excess force that overcomes the urging force of the wave washer 61 is applied to the follower 5, the follower 5 is still tilted. Furthermore, both the wave washer 61 and the stationary engaging member 62 are required in the above case, so that a number of assembling steps and a number of components to be assembled are disadvantageously increased.
Furthermore, the wiper blades are controlled to be stopped at a predetermined stop position which is generally one swing end position of the wiper blades. More specifically, when a vehicle driver manually turns off a wiper switch, the following control operation is conducted. That is, the wiper drive motor drives the wiper blades to the predetermined stop position and then stops the wiper blades in the predetermined stop position. This type of automatic stop arrangement for automatically stops the wiper blades in the predetermined stop position is disclosed in Japanese Unexamined Utility Model Publication No. 61-35068. By way of example, it will be assumed that a relatively large amount of snow is present on the windshield. In the windshield wiper system having the automatic stop arrangement, the wiper blades wipe the snow toward the predetermined stop position. When the wiper blades reach the predetermined stop position, the wiper drive motor is turned off, so that the wiper blades lose its driving force. Since the snow has been packed by the wiper blades, the snow exerts a reaction force against the wiper blades to move the wiper blades backward out of the predetermined stop position, and the wiper drive motor is forced to rotate backward. When the follower 5 is rotated backward due to the backward rotation of the wiper drive motor, a state of engagement and disengagement between the switching pattern 6 and the contact terminals 7 is changed to another state different from one that is seen while the wiper blades are held in the stop position. This change in the state of engagement and disengagement causes the wiper drive motor to drive the wiper blades toward the stop position. This results in chattering of the wiper system.
In the previously proposed rotational-position sensing device shown in FIG. 26, when the backward rotation of the wiper drive motor or the backward rotation of the wheel 2 occurs, the protrusions 8 and 9 are moved away from each other, so that the backward rotation of the wheel 2 is not transmitted to the follower 5. The prevention of the transmission of the backward rotation of the wheel 2 to the follower 5 prevents chattering of the wiper system.
However, the contact terminals 7 need to be secured to the cover 4 in manufacturing. Furthermore, the switching pattern 6 and the protrusion 9 need to be provided in the follower 5. Thus, a number of components to be assembled is increased. Because of this, parts management becomes more complicated, and a number of assembling steps is disadvantageously increased.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a rotational-position sensing device that senses a rotational position of a rotator through engagement and disengagement of contact terminals with a switching pattern based on rotation of a follower and that can be manufactured with a reduced number of assembling steps and a reduced number of components to be assembled while effectively restraining tilt of the follower. It is another objective of the present invention to provide a windshield wiper system having such a rotational-position sensing device. It is a further objective of the present invention to provide a rotational-position sensing device that restrains a change in a state of engagement and disengagement between the switching pattern and the contact terminals when the rotator is forced to rotate in a backward rotational direction and that has a reduced number of components to be assembled while achieving an improved manufacturability of the rotational-position sensing device. It is a further objective of the present invention to provide a windshield wiper system having such a rotational-position sensing device.
To achieve the objectives of the present invention, there is provided a rotational-position sensing device including a stationary body, a rotator and a follower. The stationary body includes a switching pattern. The rotator is rotatably supported by the stationary body. The rotator has a driving-side engaging means. The switching pattern is provided around a rotational axis of the rotator. The follower receives a rotational force to rotate about the rotational axis from the rotator through the driving-side engaging means. The follower is made of an electrically conductive metal plate. The follower has a plurality of contact terminals integrally formed in the electrically conductive metal plate. The follower further includes a driven-side engaging means that receives the rotational force from the rotator during rotation of the rotator in a forward rotational direction upon engagement with the driving-side engaging means in a forward rotational engaged position. The rotational-position sensing device senses a rotational position of the rotator through engagement and disengagement of the contact terminals with the switching pattern based on rotation of the follower. The driven-side engaging means has a play. The play allows the driving-side engaging means to move away from the forward rotational engaged position without transmitting the rotational force to the follower when the rotator rotates in a backward rotational direction.
To achieve the objectives of the present invention, there is also provided a windshield wiper system comprising a wiper arm with a wiper blade connected thereto, a motor and a control device. The motor has a rotational-position sensing device for sensing a rotational position of the wiper blade, a gear housing and a speed reducing mechanism. The gear housing includes a receiving recess and a cover for covering the receiving recess. The speed reducing mechanism is received within the receiving recess. The speed reducing mechanism is connected to an output shaft for outputting a rotational force of the speed reducing mechanism. The control device includes a wiper switch and controls the motor based on an operation mode selected through the wiper switch. The wiper arm and the wiper blade are reciprocally swung by a rotational driving force of the motor. The rotational-position sensing device includes a rotator, a switching pattern and a follower. The rotator is rotatably supported by the gear housing. The rotator has a driving-side engaging means and rotates integrally with the output shaft. The switching pattern is formed in the cover around a rotational axis of the rotator. The switching pattern includes a first rotational position and a second rotational position. The first rotational position corresponds to a predetermined stop position of the wiper blade. The second rotational position indicates a rotational position of the wiper blade other than the first rotational position of the wiper blade. The follower is made of an electrically conductive metal plate. The follower includes a plurality of contact terminals and a driven-side engaging means. The contact terminals are integrally formed in the electrically conductive metal plate. The contact terminals engage and disengage with the switching pattern. The driven-side engaging means receives a rotational force to rotate about the rotational axis during rotation of the rotator in a forward rotational direction upon engagement with the driving-side engaging means in a forward rotational engaged position. The driven-side engaging means has a play. The play allows the driving-side engaging means to move away from the forward rotational engaged position without transmitting the rotational force to the follower when the rotator rotates in a backward rotational direction.
To achieve the objectives of the present invention, there is also provided a rotational-position sensing device including a stationary body, a rotator, a follower, a switching pattern, a plurality of contact terminals and a space maintaining means. The rotator is rotatably supported by the stationary body. The follower is rotatably supported by a support element provided on the stationary body. The support element is coaxial with the rotator. The follower is positioned between the stationary body and the rotator and receives a rotational force from the rotator. The follower has a cylindrical engaging portion provided at a center of the follower. The cylindrical engaging portion having a peripheral surface that slidably engages a peripheral surface of the support element. The switching pattern is formed in one of the stationary body and the follower. The contact terminals are formed in the other of the stationary body and the follower. A rotational position of the rotator is sensed through engagement and disengagement of the contact terminals with the switching pattern based on rotation of the follower. A signal indicative of the rotational position of the rotator is outputted from the rotational-position sensing device. The space maintaining means is provided around the support element to maintain a predetermined space between the follower and an opposing surface of the stationary body that axially opposes the follower.
To achieve the objectives of the present invention, there is also provided a windshield wiper system including a wiper, a reciprocating swing mechanism, a motor, a speed reducing mechanism, a rotational-position sensing device and a control device. The reciprocating swing mechanism reciprocally swings the wiper. The motor has a gear housing. The speed reducing mechanism is received in the gear housing to transmit rotation of the motor at a reduced speed. The rotation of the motor is transmitted to the wiper through the speed reducing mechanism and the reciprocating swing mechanism to reciprocally swing the wiper. The rotational-position sensing device includes a rotator, a follower, a switching pattern, a plurality of contact terminals and a space maintaining means. The rotator is rotatably supported by the gear housing. The rotator is integrally rotated with an output shaft that receives a rotational force from the speed reducing mechanism. The follower is rotatably supported by a support element provided in the gear housing. The support element is coaxial with the rotator. The follower is positioned between the gear housing and the rotator and receives a rotational force from the rotator. The follower has a cylindrical engaging portion provided at a center of the follower. The cylindrical engaging portion has a peripheral surface that slidably engages a peripheral surface of the support element. The switching pattern is formed in one of the gear housing and the follower. The contact terminals are formed in the other of the gear housing and the follower. The space maintaining means is provided around the support element to maintain a predetermined space between the follower and an opposing surface of the gear housing that axially opposes the follower. The control device includes a wiper switch that is switched between a stop position and an actuation position. A rotational position of the rotator is sensed through engagement and disengagement of the contact terminals with the switching pattern based on rotation of the follower. A signal indicative of the rotational position of the rotator being outputted from the rotational-position sensing device. The control device rotates the motor until the rotational-position sensing device senses a rotational position of the rotator that corresponds to a predetermined stop position of the wiper after the wiper switch is switched to the stop position to stop the windshield wiper system. The control device stops the motor when the rotational-position sensing device senses the rotational position of the rotator that corresponds to the predetermined stop position of the wiper.